Role of vertically aligned and randomly placed zinc oxide (ZnO) nanorods in PVDF matrix: Used for energy harvesting Abhishek Anand * , M.C. Bhatnagar Department of Physics, Indian Institute of Technology, New Delhi 110016, India article info Article history: Received 14 March 2019 Received in revised form 22 May 2019 Accepted 11 June 2019 Keywords: Nanorods Nanocomposite Ferroelectric ZnO PVDF abstract The nanocomposite of ZnO nanorods and ZnO vertically aligned nanorods with polyvinyledene fluoride (PVDF) are prepared via solution casting method to make flexible and cost-effective piezoelectric nanogenerator. The structural and surface morphological studies of nanocomposite films have been carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The crys- talline polar b-phase of nanocomposite films has been evaluated by Fourier transform infrared spec- troscopy (FTIR). The results showed enhancement in this phase from 53% in PVDF to 80.6% in PVDF-ZnO vertically aligned nanorods (VANRs) nanocomposite films, respectively. The electric polarization studies showed the maximum value of remnant polarization P r is 0.2188 mC/cm 2 for PVDF-ZnO VANRs nano- composite film, measured by polarization-electric field (P-E) hysteresis loop. The value of output voltage for PVDF-ZnO VANRs is found to be 46.64 V which is more than seven times in comparison to PVDF-ZnO nanorods (NRs) based nanocomposite film generated by repeated human finger imparting on these nanocomposite films. The value of power density obtained for PVDF-ZnO VANRs is 45.87 mW/cm 2 at the load resistance of 15 MU, which can be used to drive energy to small-scale electronic appliances. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction Over the last few decades, the consumption of energy has increased tremendously due to increase in industrialization, auto- matic electronic appliances and demand. Therefore, the attention has moved towards alternate renewable energy sources such as solar energy, wind energy, wave energy and vibration energy [1e3]. However, conversion of mechanical energy into electrical energy is one the of most feasible approach in scientific community which can provide large scale of power or energy [4,5] The best way to produce self-powered device, without any restraints is to utilize piezoelectric material. The materials, having high piezoelectric properties such as lead zirconate titanate (PZT), BaTiO 3 , BiFeO 3 and ZnO with a conven- tional perovskite structure together with its compounds possessing high dielectric constant and dipole moment, are the most widely used in commercial applications [6,7]. However, due to toxicity, complex structure and complicated synthesis procedure, the use of PZT as nanofiller in PVDF matrix is avoided [8,9]. Among the lead free materials, ZnO material has paid more attention due to its excellent piezo-electric property and easy synthesis [10]. The per- formance of piezoelectric material is directly proportional to remnant polarization (P r ) of material [11]. The polymer composite of PVDF with ZnO nanorods is the most suitable material due to low electrical resistance and to make composite biocompatible, cost- effective, non-toxic and flexible [12,13]. PVDF is a very attractive polymer having light weight and highly flexible ferroelectric polymer material, which has paid much attention due to its wide range of industrial application such as charge storage material [14], electrostriction for artificial muscles [15], and smart skin for multifunctional activities [16]. PVDF and its co-polymers have been extensively studied due to its excellent environmental stability, biocompatibility and most importance its piezoelectric property. PVDF polymer exhibits higher piezoelectric coefficient among the other polymers but its poor piezo-response limits its applications. PVDF possesses five different crystal pha- ses (a, b, g, d and ε) among which (a) and (b) phases are the most relevant phase for piezoelectric and pyroelectric applications [17,18]. The non-polar a-phase, belonging to trans-gauche (TGTG 0 ), is the most common phase. On the other hand, the polar b-phase is due to all trans (TTTT) confirmation. The molecular confirmation corresponding to b-phase produces macroscopic dipole moment in definite direction, which is more attractive crystal phase in PVDF to * Corresponding author. E-mail addresses: abhishek.allen.anand@gmail.com (A. Anand), mukesh@ physics.iitd.ac.in (M.C. Bhatnagar). Contents lists available at ScienceDirect Materials Today Energy journal homepage: www.journals.elsevier.com/materials-today-energy/ https://doi.org/10.1016/j.mtener.2019.06.005 2468-6069/© 2019 Elsevier Ltd. All rights reserved. Materials Today Energy 13 (2019) 293e301